1. Field of the Invention
The present invention relates to an image processing method, a manipulation detection method, an image processing device, a manipulation detection device, an image processing program, and a manipulation detection program, all for use with an image formation medium and for detecting alteration, manipulation or interpolation of data on the image formation medium on which a latent image is formed. The present invention further relates to an image formation medium.
2. Description of the Related Art
A known method for verifying that a document has not been altered makes used of digital signatures.
Japanese Patent Laid-open Publication No. Hei 6-176036 discloses a method for creating a digital signature indicative of data and the sender of the data and for forming on an image formation medium for distribution an image in which the digital signature is embedded. A digital signature can be created through an operation using a hash function based on the main data for distribution and data on the sender. For determination as to whether or not the data has been altered, a digital signature is decoded for authentication. Besides the above-mentioned application, see Japanese Patent Laid-open Publication No. 2000-138813, Japanese Patent Laid-open Publication No. 2001-024877, and Japanese Patent Laid-open Publication No. 2000-165640, for example.)
Meanwhile, technology is known to prevent an image on an image formation medium from being copied using a copying machine. According to this technology, a latent image which becomes visible and/or clearly recognizable in the form of text or the like when the image is copied (hereinafter referred to simply as a latent image) is embedded in an image on an image formation medium. In addition, an image processing method is disclosed in which forgery prevention image information is added to data defining an image for which prohibition of copying is desired, when the image is formed on an image formation medium. The forgery prevention image data simplifies tracing of a route via which information on the image formation medium has been distributed. (See Japanese Patent Laid-open Publication No. 2001-346032, Japanese Patent Laid-open Publication No. 2001-197297, and Japanese Patent Laid-open Publication No. 2001-324898, Japanese Patent Laid-open Publication No. Hei 6-258982, and Japanese Patent Laid-open Publication No. Hei 7-231384.)
According to the above art, a latent image which becomes visible or clearly recognizable to the human eye upon copying distribution information is formed along with an image indicating the distribution data on an image formation medium. When the medium with such images is illegally copied, the latent image becomes visible or clearly recognizable such that it appears on image of the distribution information on an image formation medium of the copied version. This makes it easier to determine whether or not the image has been copied.
The above-described art which uses an image formation medium having an embedded latent image, however, has a problem such that, because a hash function operation is applied to the entire image formed on an image formation medium, which contains the latent image shown in a visible and/or clearly recognizable state as rendered during reading of the image data, whether or not the main data has been interpolated or manipulated cannot be determined.